In the field of semiconductor manufacturing, there is a continued quest for device size shrinkage. This course has led to demands for lithographic techniques to produce smaller feature sizes.
In lithographic processes using wave radiation (e.g., ultraviolet, deep ultraviolet (248 nm-KrF), far ultraviolet (193 nm-ArF), the smallest feature size that can be resolved is related to the wavelength of the imaging radiation. Real use of 193 nm lithographic processes is just starting in the microelectronics industry. Lithographic processes and tools using 157 nm radiation are envisioned, but are still years from commercial implementation. To some extent, feature size resolution with a given imaging radiation wavelength can be enhanced using alternative techniques such as bilayer lithographic processes and/or mask-related lithographic techniques (e.g., phase shift masks, etc.) Nevertheless, it is anticipated that further resolution enhancement capability (e.g., below 50 nm) will be needed for so-called next generation lithography or NGL. The likely routes for NGL are (a) so-called extreme ultraviolet (EUV) radiation lithography, (b) soft x-ray lithography, (c) electron projection lithography (EPL).
Electron beam imaging has been used in the microelectronics industry for many years in the manufacture of masks for conventional photolithography and for low volume/low throughput direct-write wafer applications. In these uses, a relatively high energy, narrow electron beam is directed precisely to selected areas of a resist layer on a mask blank or semiconductor wafer. Mask-making/direct-write processes are generally quite slow enabling accurate control of the beam position as it writes the desired pattern across the resist surface and sufficient energy transfer to the desired portions of the resist layer for subsequent development of the exposed pattern. Examples of resist materials highly suitable for use in these electron beam processes are disclosed in U.S. Pat. Nos. 6,043,003 and 6,037,097, the disclosures of which are incorporated herein by reference.
Electron projection lithography (EPL) for NGL is discussed in U.S. Pat. Nos. 4,554,458; 5,866,913; 6,069,684; 6,296,976; and 6,355,383, the disclosures of which are incorporated herein by reference. As in a conventional lithographic process, EPL involves patternwise exposure of a resist layer to imaging radiation by projecting the imaging radiation through a patterned mask. In the case of EPL, the electron projection radiation is the imaging radiation. The exposure (optionally followed by baking) induces a chemical reaction in the exposed portions of the resist which changes the solubility of the exposed regions of the resist. Thereafter, an appropriate developer, usually an aqueous base solution, is used to selectively remove the resist either in the exposed regions (positive-tone resists) or, in the unexposed region (negative-tone resists). The pattern thus defined is then imprinted on the wafer by etching away the regions that are not protected by the resist with a dry or wet etch process.
Unfortunately, EPL provides a low intensity imaging radiation such that high throughput needed for commercial semiconductor manufacture cannot be achieved with the resist materials currently available. EUV lithography and soft x-ray lithography have similar problems due to the lack of intensity of the imaging radiation. Typically, the conventional resist materials lack sufficient sensitivity, exposure dose latitude, stability (e.g., shelf-life, resistance to phase separation, stability upon vacuum exposure, etc.). Thus, there is a need for new resist compositions that can be used for EPL, EUV, soft x-ray, and other low energy intensity lithographic imaging applications.